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Revision 1.30 by root, Sat Apr 6 09:28:45 2013 UTC

… …
4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use AnyEvent::Fork; 7 use AnyEvent::Fork;
8 8
9 ################################################################## 9 AnyEvent::Fork
10 ->new
11 ->require ("MyModule")
12 ->run ("MyModule::server", my $cv = AE::cv);
13
14 my $fh = $cv->recv;
15
16=head1 DESCRIPTION
17
18This module allows you to create new processes, without actually forking
19them from your current process (avoiding the problems of forking), but
20preserving most of the advantages of fork.
21
22It can be used to create new worker processes or new independent
23subprocesses for short- and long-running jobs, process pools (e.g. for use
24in pre-forked servers) but also to spawn new external processes (such as
25CGI scripts from a web server), which can be faster (and more well behaved)
26than using fork+exec in big processes.
27
28Special care has been taken to make this module useful from other modules,
29while still supporting specialised environments such as L<App::Staticperl>
30or L<PAR::Packer>.
31
32=head1 WHAT THIS MODULE IS NOT
33
34This module only creates processes and lets you pass file handles and
35strings to it, and run perl code. It does not implement any kind of RPC -
36there is no back channel from the process back to you, and there is no RPC
37or message passing going on.
38
39If you need some form of RPC, you can either implement it yourself
40in whatever way you like, use some message-passing module such
41as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
42L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
43and so on.
44
45=head1 PROBLEM STATEMENT
46
47There are two traditional ways to implement parallel processing on UNIX
48like operating systems - fork and process, and fork+exec and process. They
49have different advantages and disadvantages that I describe below,
50together with how this module tries to mitigate the disadvantages.
51
52=over 4
53
54=item Forking from a big process can be very slow.
55
56A 5GB process needs 0.05s to fork on my 3.6GHz amd64 GNU/Linux box. This
57overhead is often shared with exec (because you have to fork first), but
58in some circumstances (e.g. when vfork is used), fork+exec can be much
59faster.
60
61This module can help here by telling a small(er) helper process to fork,
62which is faster then forking the main process, and also uses vfork where
63possible. This gives the speed of vfork, with the flexibility of fork.
64
65=item Forking usually creates a copy-on-write copy of the parent
66process.
67
68For example, modules or data files that are loaded will not use additional
69memory after a fork. When exec'ing a new process, modules and data files
70might need to be loaded again, at extra CPU and memory cost. But when
71forking, literally all data structures are copied - if the program frees
72them and replaces them by new data, the child processes will retain the
73old version even if it isn't used, which can suddenly and unexpectedly
74increase memory usage when freeing memory.
75
76The trade-off is between more sharing with fork (which can be good or
77bad), and no sharing with exec.
78
79This module allows the main program to do a controlled fork, and allows
80modules to exec processes safely at any time. When creating a custom
81process pool you can take advantage of data sharing via fork without
82risking to share large dynamic data structures that will blow up child
83memory usage.
84
85In other words, this module puts you into control over what is being
86shared and what isn't, at all times.
87
88=item Exec'ing a new perl process might be difficult.
89
90For example, it is not easy to find the correct path to the perl
91interpreter - C<$^X> might not be a perl interpreter at all.
92
93This module tries hard to identify the correct path to the perl
94interpreter. With a cooperative main program, exec'ing the interpreter
95might not even be necessary, but even without help from the main program,
96it will still work when used from a module.
97
98=item Exec'ing a new perl process might be slow, as all necessary modules
99have to be loaded from disk again, with no guarantees of success.
100
101Long running processes might run into problems when perl is upgraded
102and modules are no longer loadable because they refer to a different
103perl version, or parts of a distribution are newer than the ones already
104loaded.
105
106This module supports creating pre-initialised perl processes to be used as
107a template for new processes.
108
109=item Forking might be impossible when a program is running.
110
111For example, POSIX makes it almost impossible to fork from a
112multi-threaded program while doing anything useful in the child - in
113fact, if your perl program uses POSIX threads (even indirectly via
114e.g. L<IO::AIO> or L<threads>), you cannot call fork on the perl level
115anymore without risking corruption issues on a number of operating
116systems.
117
118This module can safely fork helper processes at any time, by calling
119fork+exec in C, in a POSIX-compatible way (via L<Proc::FastSpawn>).
120
121=item Parallel processing with fork might be inconvenient or difficult
122to implement. Modules might not work in both parent and child.
123
124For example, when a program uses an event loop and creates watchers it
125becomes very hard to use the event loop from a child program, as the
126watchers already exist but are only meaningful in the parent. Worse, a
127module might want to use such a module, not knowing whether another module
128or the main program also does, leading to problems.
129
130Apart from event loops, graphical toolkits also commonly fall into the
131"unsafe module" category, or just about anything that communicates with
132the external world, such as network libraries and file I/O modules, which
133usually don't like being copied and then allowed to continue in two
134processes.
135
136With this module only the main program is allowed to create new processes
137by forking (because only the main program can know when it is still safe
138to do so) - all other processes are created via fork+exec, which makes it
139possible to use modules such as event loops or window interfaces safely.
140
141=back
142
143=head1 EXAMPLES
144
10 # create a single new process, tell it to run your worker function 145=head2 Create a single new process, tell it to run your worker function.
11 146
12 AnyEvent::Fork 147 AnyEvent::Fork
13 ->new 148 ->new
14 ->require ("MyModule") 149 ->require ("MyModule")
15 ->run ("MyModule::worker, sub { 150 ->run ("MyModule::worker, sub {
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17 152
18 # now $master_filehandle is connected to the 153 # now $master_filehandle is connected to the
19 # $slave_filehandle in the new process. 154 # $slave_filehandle in the new process.
20 }); 155 });
21 156
22 # MyModule::worker might look like this 157MyModule::worker might look like this:
158
23 sub MyModule::worker { 159 sub MyModule::worker {
24 my ($slave_filehandle) = @_; 160 my ($slave_filehandle) = @_;
25 161
26 # now $slave_filehandle is connected to the $master_filehandle 162 # now $slave_filehandle is connected to the $master_filehandle
27 # in the original prorcess. have fun! 163 # in the original prorcess. have fun!
28 } 164 }
29 165
30 ##################################################################
31 # create a pool of server processes all accepting on the same socket 166=head2 Create a pool of server processes all accepting on the same socket.
32 167
33 # create listener socket 168 # create listener socket
34 my $listener = ...; 169 my $listener = ...;
35 170
36 # create a pool template, initialise it and give it the socket 171 # create a pool template, initialise it and give it the socket
… …
48 } 183 }
49 184
50 # now do other things - maybe use the filehandle provided by run 185 # now do other things - maybe use the filehandle provided by run
51 # to wait for the processes to die. or whatever. 186 # to wait for the processes to die. or whatever.
52 187
53 # My::Server::run might look like this 188My::Server::run might look like this:
189
54 sub My::Server::run { 190 sub My::Server::run {
55 my ($slave, $listener, $id) = @_; 191 my ($slave, $listener, $id) = @_;
56 192
57 close $slave; # we do not use the socket, so close it to save resources 193 close $slave; # we do not use the socket, so close it to save resources
58 194
… …
61 while (my $socket = $listener->accept) { 197 while (my $socket = $listener->accept) {
62 # do sth. with new socket 198 # do sth. with new socket
63 } 199 }
64 } 200 }
65 201
66=head1 DESCRIPTION 202=head2 use AnyEvent::Fork as a faster fork+exec
67 203
68This module allows you to create new processes, without actually forking 204This runs /bin/echo hi, with stdout redirected to /tmp/log and stderr to
69them from your current process (avoiding the problems of forking), but 205the communications socket. It is usually faster than fork+exec, but still
70preserving most of the advantages of fork. 206let's you prepare the environment.
71 207
72It can be used to create new worker processes or new independent 208 open my $output, ">/tmp/log" or die "$!";
73subprocesses for short- and long-running jobs, process pools (e.g. for use
74in pre-forked servers) but also to spawn new external processes (such as
75CGI scripts from a webserver), which can be faster (and more well behaved)
76than using fork+exec in big processes.
77 209
78Special care has been taken to make this module useful from other modules, 210 AnyEvent::Fork
79while still supporting specialised environments such as L<App::Staticperl> 211 ->new
80or L<PAR::Packer>. 212 ->eval ('
213 sub run {
214 my ($fh, $output, @cmd) = @_;
81 215
82=head1 WHAT THIS MODULE IS NOT 216 # perl will clear close-on-exec on STDOUT/STDERR
217 open STDOUT, ">&", $output or die;
218 open STDERR, ">&", $fh or die;
83 219
84This module only creates processes and lets you pass file handles and 220 exec @cmd;
85strings to it, and run perl code. It does not implement any kind of RPC - 221 }
86there is no back channel from the process back to you, and there is no RPC 222 ')
87or message passing going on. 223 ->send_fh ($output)
224 ->send_arg ("/bin/echo", "hi")
225 ->run ("run", my $cv = AE::cv);
88 226
89If you need some form of RPC, you can either implement it yourself 227 my $stderr = $cv->recv;
90in whatever way you like, use some message-passing module such
91as L<AnyEvent::MP>, some pipe such as L<AnyEvent::ZeroMQ>, use
92L<AnyEvent::Handle> on both sides to send e.g. JSON or Storable messages,
93and so on.
94
95=head1 PROBLEM STATEMENT
96
97There are two ways to implement parallel processing on UNIX like operating
98systems - fork and process, and fork+exec and process. They have different
99advantages and disadvantages that I describe below, together with how this
100module tries to mitigate the disadvantages.
101
102=over 4
103
104=item Forking from a big process can be very slow (a 5GB process needs
1050.05s to fork on my 3.6GHz amd64 GNU/Linux box for example). This overhead
106is often shared with exec (because you have to fork first), but in some
107circumstances (e.g. when vfork is used), fork+exec can be much faster.
108
109This module can help here by telling a small(er) helper process to fork,
110or fork+exec instead.
111
112=item Forking usually creates a copy-on-write copy of the parent
113process. Memory (for example, modules or data files that have been
114will not take additional memory). When exec'ing a new process, modules
115and data files might need to be loaded again, at extra cpu and memory
116cost. Likewise when forking, all data structures are copied as well - if
117the program frees them and replaces them by new data, the child processes
118will retain the memory even if it isn't used.
119
120This module allows the main program to do a controlled fork, and allows
121modules to exec processes safely at any time. When creating a custom
122process pool you can take advantage of data sharing via fork without
123risking to share large dynamic data structures that will blow up child
124memory usage.
125
126=item Exec'ing a new perl process might be difficult and slow. For
127example, it is not easy to find the correct path to the perl interpreter,
128and all modules have to be loaded from disk again. Long running processes
129might run into problems when perl is upgraded for example.
130
131This module supports creating pre-initialised perl processes to be used
132as template, and also tries hard to identify the correct path to the perl
133interpreter. With a cooperative main program, exec'ing the interpreter
134might not even be necessary.
135
136=item Forking might be impossible when a program is running. For example,
137POSIX makes it almost impossible to fork from a multithreaded program and
138do anything useful in the child - strictly speaking, if your perl program
139uses posix threads (even indirectly via e.g. L<IO::AIO> or L<threads>),
140you cannot call fork on the perl level anymore, at all.
141
142This module can safely fork helper processes at any time, by caling
143fork+exec in C, in a POSIX-compatible way.
144
145=item Parallel processing with fork might be inconvenient or difficult
146to implement. For example, when a program uses an event loop and creates
147watchers it becomes very hard to use the event loop from a child
148program, as the watchers already exist but are only meaningful in the
149parent. Worse, a module might want to use such a system, not knowing
150whether another module or the main program also does, leading to problems.
151
152This module only lets the main program create pools by forking (because
153only the main program can know when it is still safe to do so) - all other
154pools are created by fork+exec, after which such modules can again be
155loaded.
156
157=back
158 228
159=head1 CONCEPTS 229=head1 CONCEPTS
160 230
161This module can create new processes either by executing a new perl 231This module can create new processes either by executing a new perl
162process, or by forking from an existing "template" process. 232process, or by forking from an existing "template" process.
… …
179needed the first time. Forking from this process shares the memory used 249needed the first time. Forking from this process shares the memory used
180for the perl interpreter with the new process, but loading modules takes 250for the perl interpreter with the new process, but loading modules takes
181time, and the memory is not shared with anything else. 251time, and the memory is not shared with anything else.
182 252
183This is ideal for when you only need one extra process of a kind, with the 253This is ideal for when you only need one extra process of a kind, with the
184option of starting and stipping it on demand. 254option of starting and stopping it on demand.
185 255
186Example: 256Example:
187 257
188 AnyEvent::Fork 258 AnyEvent::Fork
189 ->new 259 ->new
… …
204modules you loaded) is shared between the processes, and each new process 274modules you loaded) is shared between the processes, and each new process
205consumes relatively little memory of its own. 275consumes relatively little memory of its own.
206 276
207The disadvantage of this approach is that you need to create a template 277The disadvantage of this approach is that you need to create a template
208process for the sole purpose of forking new processes from it, but if you 278process for the sole purpose of forking new processes from it, but if you
209only need a fixed number of proceses you can create them, and then destroy 279only need a fixed number of processes you can create them, and then destroy
210the template process. 280the template process.
211 281
212Example: 282Example:
213 283
214 my $template = AnyEvent::Fork->new->require ("Some::Module"); 284 my $template = AnyEvent::Fork->new->require ("Some::Module");
… …
241 my ($fork_fh) = @_; 311 my ($fork_fh) = @_;
242 }); 312 });
243 313
244=back 314=back
245 315
246=head1 FUNCTIONS 316=head1 THE C<AnyEvent::Fork> CLASS
317
318This module exports nothing, and only implements a single class -
319C<AnyEvent::Fork>.
320
321There are two class constructors that both create new processes - C<new>
322and C<new_exec>. The C<fork> method creates a new process by forking an
323existing one and could be considered a third constructor.
324
325Most of the remaining methods deal with preparing the new process, by
326loading code, evaluating code and sending data to the new process. They
327usually return the process object, so you can chain method calls.
328
329If a process object is destroyed before calling its C<run> method, then
330the process simply exits. After C<run> is called, all responsibility is
331passed to the specified function.
332
333As long as there is any outstanding work to be done, process objects
334resist being destroyed, so there is no reason to store them unless you
335need them later - configure and forget works just fine.
247 336
248=over 4 337=over 4
249 338
250=cut 339=cut
251 340
252package AnyEvent::Fork; 341package AnyEvent::Fork;
253 342
254use common::sense; 343use common::sense;
255 344
256use Socket (); 345use Errno ();
257 346
258use AnyEvent; 347use AnyEvent;
259use AnyEvent::Util (); 348use AnyEvent::Util ();
260 349
261use IO::FDPass; 350use IO::FDPass;
262 351
263our $VERSION = 0.2; 352our $VERSION = 0.5;
264 353
265our $PERL; # the path to the perl interpreter, deduces with various forms of magic 354our $PERL; # the path to the perl interpreter, deduces with various forms of magic
266
267=item my $pool = new AnyEvent::Fork key => value...
268
269Create a new process pool. The following named parameters are supported:
270 355
271=over 4 356=over 4
272 357
273=back 358=back
274 359
… …
281our $TEMPLATE; 366our $TEMPLATE;
282 367
283sub _cmd { 368sub _cmd {
284 my $self = shift; 369 my $self = shift;
285 370
286 #TODO: maybe append the packet to any existing string command already in the queue
287
288 # ideally, we would want to use "a (w/a)*" as format string, but perl versions 371 # ideally, we would want to use "a (w/a)*" as format string, but perl
289 # from at least 5.8.9 to 5.16.3 are all buggy and can't unpack it. 372 # versions from at least 5.8.9 to 5.16.3 are all buggy and can't unpack
373 # it.
290 push @{ $self->[2] }, pack "L/a*", pack "(w/a*)*", @_; 374 push @{ $self->[2] }, pack "a L/a*", $_[0], $_[1];
291 375
292 $self->[3] ||= AE::io $self->[1], 1, sub { 376 $self->[3] ||= AE::io $self->[1], 1, sub {
377 do {
293 # send the next "thing" in the queue - either a reference to an fh, 378 # send the next "thing" in the queue - either a reference to an fh,
294 # or a plain string. 379 # or a plain string.
295 380
296 if (ref $self->[2][0]) { 381 if (ref $self->[2][0]) {
297 # send fh 382 # send fh
298 IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] } 383 unless (IO::FDPass::send fileno $self->[1], fileno ${ $self->[2][0] }) {
384 return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK;
385 undef $self->[3];
386 die "AnyEvent::Fork: file descriptor send failure: $!";
387 }
388
299 and shift @{ $self->[2] }; 389 shift @{ $self->[2] };
300 390
301 } else { 391 } else {
302 # send string 392 # send string
303 my $len = syswrite $self->[1], $self->[2][0] 393 my $len = syswrite $self->[1], $self->[2][0];
394
395 unless ($len) {
396 return if $! == Errno::EAGAIN || $! == Errno::EWOULDBLOCK;
397 undef $self->[3];
304 or do { undef $self->[3]; die "AnyEvent::Fork: command write failure: $!" }; 398 die "AnyEvent::Fork: command write failure: $!";
399 }
305 400
306 substr $self->[2][0], 0, $len, ""; 401 substr $self->[2][0], 0, $len, "";
307 shift @{ $self->[2] } unless length $self->[2][0]; 402 shift @{ $self->[2] } unless length $self->[2][0];
308 } 403 }
404 } while @{ $self->[2] };
309 405
310 unless (@{ $self->[2] }) { 406 # everything written
311 undef $self->[3]; 407 undef $self->[3];
408
312 # invoke run callback 409 # invoke run callback, if any
313 $self->[0]->($self->[1]) if $self->[0]; 410 $self->[4]->($self->[1]) if $self->[4];
314 }
315 }; 411 };
316 412
317 () # make sure we don't leak the watcher 413 () # make sure we don't leak the watcher
318} 414}
319 415
320sub _new { 416sub _new {
321 my ($self, $fh) = @_; 417 my ($self, $fh, $pid) = @_;
322 418
323 AnyEvent::Util::fh_nonblocking $fh, 1; 419 AnyEvent::Util::fh_nonblocking $fh, 1;
324 420
325 $self = bless [ 421 $self = bless [
326 undef, # run callback 422 $pid,
327 $fh, 423 $fh,
328 [], # write queue - strings or fd's 424 [], # write queue - strings or fd's
329 undef, # AE watcher 425 undef, # AE watcher
330 ], $self; 426 ], $self;
331 427
… …
349 exit 0; 445 exit 0;
350 } elsif (!$pid) { 446 } elsif (!$pid) {
351 die "AnyEvent::Fork::Early/Template: unable to fork template process: $!"; 447 die "AnyEvent::Fork::Early/Template: unable to fork template process: $!";
352 } 448 }
353 449
354 AnyEvent::Fork->_new ($fh) 450 AnyEvent::Fork->_new ($fh, $pid)
355} 451}
356 452
357=item my $proc = new AnyEvent::Fork 453=item my $proc = new AnyEvent::Fork
358 454
359Create a new "empty" perl interpreter process and returns its process 455Create a new "empty" perl interpreter process and returns its process
360object for further manipulation. 456object for further manipulation.
361 457
362The new process is forked from a template process that is kept around 458The new process is forked from a template process that is kept around
363for this purpose. When it doesn't exist yet, it is created by a call to 459for this purpose. When it doesn't exist yet, it is created by a call to
364C<new_exec> and kept around for future calls. 460C<new_exec> first and then stays around for future calls.
365
366When the process object is destroyed, it will release the file handle
367that connects it with the new process. When the new process has not yet
368called C<run>, then the process will exit. Otherwise, what happens depends
369entirely on the code that is executed.
370 461
371=cut 462=cut
372 463
373sub new { 464sub new {
374 my $class = shift; 465 my $class = shift;
… …
410reduces the amount of memory sharing that is possible, and is also slower. 501reduces the amount of memory sharing that is possible, and is also slower.
411 502
412You should use C<new> whenever possible, except when having a template 503You should use C<new> whenever possible, except when having a template
413process around is unacceptable. 504process around is unacceptable.
414 505
415The path to the perl interpreter is divined usign various methods - first 506The path to the perl interpreter is divined using various methods - first
416C<$^X> is investigated to see if the path ends with something that sounds 507C<$^X> is investigated to see if the path ends with something that sounds
417as if it were the perl interpreter. Failing this, the module falls back to 508as if it were the perl interpreter. Failing this, the module falls back to
418using C<$Config::Config{perlpath}>. 509using C<$Config::Config{perlpath}>.
419 510
420=cut 511=cut
… …
452 # quick. also doesn't work in win32. of course. what did you expect 543 # quick. also doesn't work in win32. of course. what did you expect
453 #local $ENV{PERL5LIB} = join ":", grep !ref, @INC; 544 #local $ENV{PERL5LIB} = join ":", grep !ref, @INC;
454 my %env = %ENV; 545 my %env = %ENV;
455 $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC; 546 $env{PERL5LIB} = join +($^O eq "MSWin32" ? ";" : ":"), grep !ref, @INC;
456 547
457 Proc::FastSpawn::spawn ( 548 my $pid = Proc::FastSpawn::spawn (
458 $perl, 549 $perl,
459 ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$], 550 ["perl", "-MAnyEvent::Fork::Serve", "-e", "AnyEvent::Fork::Serve::me", fileno $slave, $$],
460 [map "$_=$env{$_}", keys %env], 551 [map "$_=$env{$_}", keys %env],
461 ) or die "unable to spawn AnyEvent::Fork server: $!"; 552 ) or die "unable to spawn AnyEvent::Fork server: $!";
462 553
463 $self->_new ($fh) 554 $self->_new ($fh, $pid)
555}
556
557=item $pid = $proc->pid
558
559Returns the process id of the process I<iff it is a direct child of the
560process> running AnyEvent::Fork, and C<undef> otherwise.
561
562Normally, only processes created via C<< AnyEvent::Fork->new_exec >> and
563L<AnyEvent::Fork::Template> are direct children, and you are responsible
564to clean up their zombies when they die.
565
566All other processes are not direct children, and will be cleaned up by
567AnyEvent::Fork itself.
568
569=cut
570
571sub pid {
572 $_[0][0]
464} 573}
465 574
466=item $proc = $proc->eval ($perlcode, @args) 575=item $proc = $proc->eval ($perlcode, @args)
467 576
468Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to 577Evaluates the given C<$perlcode> as ... perl code, while setting C<@_> to
469the strings specified by C<@args>. 578the strings specified by C<@args>, in the "main" package.
470 579
471This call is meant to do any custom initialisation that might be required 580This call is meant to do any custom initialisation that might be required
472(for example, the C<require> method uses it). It's not supposed to be used 581(for example, the C<require> method uses it). It's not supposed to be used
473to completely take over the process, use C<run> for that. 582to completely take over the process, use C<run> for that.
474 583
475The code will usually be executed after this call returns, and there is no 584The code will usually be executed after this call returns, and there is no
476way to pass anything back to the calling process. Any evaluation errors 585way to pass anything back to the calling process. Any evaluation errors
477will be reported to stderr and cause the process to exit. 586will be reported to stderr and cause the process to exit.
478 587
588If you want to execute some code to take over the process (see the
589"fork+exec" example in the SYNOPSIS), you should compile a function via
590C<eval> first, and then call it via C<run>. This also gives you access to
591any arguments passed via the C<send_xxx> methods, such as file handles.
592
479Returns the process object for easy chaining of method calls. 593Returns the process object for easy chaining of method calls.
480 594
481=cut 595=cut
482 596
483sub eval { 597sub eval {
484 my ($self, $code, @args) = @_; 598 my ($self, $code, @args) = @_;
485 599
486 $self->_cmd (e => $code, @args); 600 $self->_cmd (e => pack "(w/a*)*", $code, @args);
487 601
488 $self 602 $self
489} 603}
490 604
491=item $proc = $proc->require ($module, ...) 605=item $proc = $proc->require ($module, ...)
… …
515accomplished by simply not storing the file handles anywhere after passing 629accomplished by simply not storing the file handles anywhere after passing
516them to this method. 630them to this method.
517 631
518Returns the process object for easy chaining of method calls. 632Returns the process object for easy chaining of method calls.
519 633
520Example: pass an fh to a process, and release it without closing. it will 634Example: pass a file handle to a process, and release it without
521be closed automatically when it is no longer used. 635closing. It will be closed automatically when it is no longer used.
522 636
523 $proc->send_fh ($my_fh); 637 $proc->send_fh ($my_fh);
524 undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT 638 undef $my_fh; # free the reference if you want, but DO NOT CLOSE IT
525 639
526=cut 640=cut
… …
539=item $proc = $proc->send_arg ($string, ...) 653=item $proc = $proc->send_arg ($string, ...)
540 654
541Send one or more argument strings to the process, to prepare a call to 655Send one or more argument strings to the process, to prepare a call to
542C<run>. The strings can be any octet string. 656C<run>. The strings can be any octet string.
543 657
658The protocol is optimised to pass a moderate number of relatively short
659strings - while you can pass up to 4GB of data in one go, this is more
660meant to pass some ID information or other startup info, not big chunks of
661data.
662
544Returns the process object for easy chaining of emthod calls. 663Returns the process object for easy chaining of method calls.
545 664
546=cut 665=cut
547 666
548sub send_arg { 667sub send_arg {
549 my ($self, @arg) = @_; 668 my ($self, @arg) = @_;
550 669
551 $self->_cmd (a => @arg); 670 $self->_cmd (a => pack "(w/a*)*", @arg);
552 671
553 $self 672 $self
554} 673}
555 674
556=item $proc->run ($func, $cb->($fh)) 675=item $proc->run ($func, $cb->($fh))
557 676
558Enter the function specified by the fully qualified name in C<$func> in 677Enter the function specified by the function name in C<$func> in the
559the process. The function is called with the communication socket as first 678process. The function is called with the communication socket as first
560argument, followed by all file handles and string arguments sent earlier 679argument, followed by all file handles and string arguments sent earlier
561via C<send_fh> and C<send_arg> methods, in the order they were called. 680via C<send_fh> and C<send_arg> methods, in the order they were called.
562 681
563If the called function returns, the process exits. 682The function name should be fully qualified, but if it isn't, it will be
683looked up in the main package.
564 684
565Preparing the process can take time - when the process is ready, the 685If the called function returns, doesn't exist, or any error occurs, the
686process exits.
687
688Preparing the process is done in the background - when all commands have
566callback is invoked with the local communications socket as argument. 689been sent, the callback is invoked with the local communications socket
690as argument. At this point you can start using the socket in any way you
691like.
567 692
568The process object becomes unusable on return from this function. 693The process object becomes unusable on return from this function - any
694further method calls result in undefined behaviour.
569 695
570If the communication socket isn't used, it should be closed on both sides, 696If the communication socket isn't used, it should be closed on both sides,
571to save on kernel memory. 697to save on kernel memory.
572 698
573The socket is non-blocking in the parent, and blocking in the newly 699The socket is non-blocking in the parent, and blocking in the newly
574created process. The close-on-exec flag is set on both. Even if not used 700created process. The close-on-exec flag is set in both.
701
575otherwise, the socket can be a good indicator for the existance of the 702Even if not used otherwise, the socket can be a good indicator for the
576process - if the other process exits, you get a readable event on it, 703existence of the process - if the other process exits, you get a readable
577because exiting the process closes the socket (if it didn't create any 704event on it, because exiting the process closes the socket (if it didn't
578children using fork). 705create any children using fork).
579 706
580Example: create a template for a process pool, pass a few strings, some 707Example: create a template for a process pool, pass a few strings, some
581file handles, then fork, pass one more string, and run some code. 708file handles, then fork, pass one more string, and run some code.
582 709
583 my $pool = AnyEvent::Fork 710 my $pool = AnyEvent::Fork
… …
591 ->send_arg ("str3") 718 ->send_arg ("str3")
592 ->run ("Some::function", sub { 719 ->run ("Some::function", sub {
593 my ($fh) = @_; 720 my ($fh) = @_;
594 721
595 # fh is nonblocking, but we trust that the OS can accept these 722 # fh is nonblocking, but we trust that the OS can accept these
596 # extra 3 octets anyway. 723 # few octets anyway.
597 syswrite $fh, "hi #$_\n"; 724 syswrite $fh, "hi #$_\n";
598 725
599 # $fh is being closed here, as we don't store it anywhere 726 # $fh is being closed here, as we don't store it anywhere
600 }); 727 });
601 } 728 }
… …
603 # Some::function might look like this - all parameters passed before fork 730 # Some::function might look like this - all parameters passed before fork
604 # and after will be passed, in order, after the communications socket. 731 # and after will be passed, in order, after the communications socket.
605 sub Some::function { 732 sub Some::function {
606 my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_; 733 my ($fh, $str1, $str2, $fh1, $fh2, $str3) = @_;
607 734
608 print scalar <$fh>; # prints "hi 1\n" and "hi 2\n" 735 print scalar <$fh>; # prints "hi #1\n" and "hi #2\n" in any order
609 } 736 }
610 737
611=cut 738=cut
612 739
613sub run { 740sub run {
614 my ($self, $func, $cb) = @_; 741 my ($self, $func, $cb) = @_;
615 742
616 $self->[0] = $cb; 743 $self->[4] = $cb;
617 $self->_cmd (r => $func); 744 $self->_cmd (r => $func);
618} 745}
619 746
620=back 747=back
621 748
622=head1 PERFORMANCE 749=head1 PERFORMANCE
623 750
624Now for some unscientific benchmark numbers (all done on an amd64 751Now for some unscientific benchmark numbers (all done on an amd64
625GNU/Linux box). These are intended to give you an idea of the relative 752GNU/Linux box). These are intended to give you an idea of the relative
626performance you can expect. 753performance you can expect, they are not meant to be absolute performance
754numbers.
627 755
628Ok, so, I ran a simple benchmark that creates a socketpair, forks, calls 756OK, so, I ran a simple benchmark that creates a socket pair, forks, calls
629exit in the child and waits for the socket to close in the parent. I did 757exit in the child and waits for the socket to close in the parent. I did
630load AnyEvent, EV and AnyEvent::Fork, for a total process size of 6312kB. 758load AnyEvent, EV and AnyEvent::Fork, for a total process size of 5100kB.
631 759
632 2079 new processes per second, using socketpair + fork manually 760 2079 new processes per second, using manual socketpair + fork
633 761
634Then I did the same thing, but instead of calling fork, I called 762Then I did the same thing, but instead of calling fork, I called
635AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the 763AnyEvent::Fork->new->run ("CORE::exit") and then again waited for the
636socket form the child to close on exit. This does the same thing as manual 764socket form the child to close on exit. This does the same thing as manual
637socketpair + fork, except that what is forked is the template process 765socket pair + fork, except that what is forked is the template process
638(2440kB), and the socket needs to be passed to the server at the other end 766(2440kB), and the socket needs to be passed to the server at the other end
639of the socket first. 767of the socket first.
640 768
641 2307 new processes per second, using AnyEvent::Fork->new 769 2307 new processes per second, using AnyEvent::Fork->new
642 770
643And finally, using C<new_exec> instead C<new>, using vforks+execs to exec 771And finally, using C<new_exec> instead C<new>, using vforks+execs to exec
644a new perl interpreter and compile the small server each time, I get: 772a new perl interpreter and compile the small server each time, I get:
645 773
646 479 vfork+execs per second, using AnyEvent::Fork->new_exec 774 479 vfork+execs per second, using AnyEvent::Fork->new_exec
647 775
648So how can C<< AnyEvent->new >> be faster than a standard fork, een though 776So how can C<< AnyEvent->new >> be faster than a standard fork, even
649it uses the same operations, but adds a lot of overhead? 777though it uses the same operations, but adds a lot of overhead?
650 778
651The difference is simply the process size: forking the 6MB process takes 779The difference is simply the process size: forking the 6MB process takes
652so much longer than forking the 2.5MB template process that the overhead 780so much longer than forking the 2.5MB template process that the overhead
653introduced is canceled out. 781introduced is canceled out.
654 782
… …
656 784
657 1340 new processes, manual fork in a 20MB process 785 1340 new processes, manual fork in a 20MB process
658 731 new processes, manual fork in a 200MB process 786 731 new processes, manual fork in a 200MB process
659 235 new processes, manual fork in a 2000MB process 787 235 new processes, manual fork in a 2000MB process
660 788
661What that means (to me) is that I can use this module without havign a 789What that means (to me) is that I can use this module without having a
662very bad conscience because of the extra overhead requried to strat new 790very bad conscience because of the extra overhead required to start new
663processes. 791processes.
664 792
665=head1 TYPICAL PROBLEMS 793=head1 TYPICAL PROBLEMS
666 794
667This section lists typical problems that remain. I hope by recognising 795This section lists typical problems that remain. I hope by recognising
… …
675process. While perl itself laudably sets the close-on-exec flags on new 803process. While perl itself laudably sets the close-on-exec flags on new
676file handles, most C libraries don't care, and even if all cared, it's 804file handles, most C libraries don't care, and even if all cared, it's
677often not possible to set the flag in a race-free manner. 805often not possible to set the flag in a race-free manner.
678 806
679That means some file descriptors can leak through. And since it isn't 807That means some file descriptors can leak through. And since it isn't
680possible to know which file descriptors are "good" and "neccessary" (or 808possible to know which file descriptors are "good" and "necessary" (or
681even to know which file descreiptors are open), there is no good way to 809even to know which file descriptors are open), there is no good way to
682close the ones that might harm. 810close the ones that might harm.
683 811
684As an example of what "harm" can be done consider a web server that 812As an example of what "harm" can be done consider a web server that
685accepts connections and afterwards some module uses AnyEvent::Fork for the 813accepts connections and afterwards some module uses AnyEvent::Fork for the
686first time, causing it to fork and exec a new process, which might inherit 814first time, causing it to fork and exec a new process, which might inherit
… …
694well before many random file descriptors are open. 822well before many random file descriptors are open.
695 823
696In general, the solution for these kind of problems is to fix the 824In general, the solution for these kind of problems is to fix the
697libraries or the code that leaks those file descriptors. 825libraries or the code that leaks those file descriptors.
698 826
699Fortunately, most of these lekaed descriptors do no harm, other than 827Fortunately, most of these leaked descriptors do no harm, other than
700sitting on some resources. 828sitting on some resources.
701 829
702=item "leaked" file descriptors for fork'ed processes 830=item "leaked" file descriptors for fork'ed processes
703 831
704Normally, L<AnyEvent::Fork> does start new processes by exec'ing them, 832Normally, L<AnyEvent::Fork> does start new processes by exec'ing them,
… …
716 844
717The solution is to either not load these modules before use'ing 845The solution is to either not load these modules before use'ing
718L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay 846L<AnyEvent::Fork::Early> or L<AnyEvent::Fork::Template>, or to delay
719initialising them, for example, by calling C<init Gtk2> manually. 847initialising them, for example, by calling C<init Gtk2> manually.
720 848
849=item exit runs destructors
850
851This only applies to users of Lc<AnyEvent::Fork:Early> and
852L<AnyEvent::Fork::Template>.
853
854When a process created by AnyEvent::Fork exits, it might do so by calling
855exit, or simply letting perl reach the end of the program. At which point
856Perl runs all destructors.
857
858Not all destructors are fork-safe - for example, an object that represents
859the connection to an X display might tell the X server to free resources,
860which is inconvenient when the "real" object in the parent still needs to
861use them.
862
863This is obviously not a problem for L<AnyEvent::Fork::Early>, as you used
864it as the very first thing, right?
865
866It is a problem for L<AnyEvent::Fork::Template> though - and the solution
867is to not create objects with nontrivial destructors that might have an
868effect outside of Perl.
869
721=back 870=back
722 871
723=head1 PORTABILITY NOTES 872=head1 PORTABILITY NOTES
724 873
725Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop, 874Native win32 perls are somewhat supported (AnyEvent::Fork::Early is a nop,
726and ::Template is not going to work), and it cost a lot of blood and sweat 875and ::Template is not going to work), and it cost a lot of blood and sweat
727to make it so, mostly due to the bloody broken perl that nobody seems to 876to make it so, mostly due to the bloody broken perl that nobody seems to
728care about. The fork emulation is a bad joke - I have yet to see something 877care about. The fork emulation is a bad joke - I have yet to see something
729useful that you cna do with it without running into memory corruption 878useful that you can do with it without running into memory corruption
730issues or other braindamage. Hrrrr. 879issues or other braindamage. Hrrrr.
731 880
732Cygwin perl is not supported at the moment, as it should implement fd 881Cygwin perl is not supported at the moment, as it should implement fd
733passing, but doesn't, and rolling my own is hard, as cygwin doesn't 882passing, but doesn't, and rolling my own is hard, as cygwin doesn't
734support enough functionality to do it. 883support enough functionality to do it.

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